This invention relates to the field of deterioration prediction, more specifically to predicting the rate of deterioration in one or more items of process equipment from one or more feedstock properties.
Corrosion is a pervasive problem in the refining of crude oil, and necessitates the constant monitoring and inspection of the various processing units within a refinery. Often, the refinery units need to be fabricated from expensive corrosion-resistant materials in order to have sufficient lifetime before replacement, particularly units which are exposed to high temperatures and corrosive compositions.
Different crude oils are known to have different corrosive properties. Typical sources of corrosion from crude oils include the presence of one or more of oxygen, water, acidic species such as naphthenic acids, or other reactive species such as sulphur-containing compounds.
Over time, a large body of information has been collated on the types of corrosion experienced in various refinery units, based on the materials of construction of the refinery units. Such data have been published, for example by the American Petroleum Institute in document API-581.
API-581 comprises, inter alia, means for estimating the lifetime of a refinery unit from the extent and nature of visible corrosion present within the unit, based on the materials of construction and the function or duty which it performs. However, the model is only an estimate, and is not necessarily capable of predicting the corrosion rate of a freshly installed, corrosion-free unit, nor is it capable of estimating the extent of corrosion when different types of crude oil having different corrosion properties are fed to the refinery. The models are therefore not always accurate, and can result in unplanned shutdowns due to the unexpected need to repair or replace a corroded unit earlier than planned.
Another problem experienced in crude oil refineries is the deactivation of catalysts, which can be used in several refining processes such as fluid catalytic cracking, catalytic reforming, hydrocracking and hydrodesulphurisation. Not only do different crude oils have different effects on the type and rate of corrosion, for example, but also they can have different effects on the rate of catalyst deactivation. Although catalyst lifetimes can be estimated to some extent based on experience, the estimates typically do not encompass the effects of using different feedstocks throughout the catalyst lifetime. The potential for the early and unexpected need to replace or regenerate a prematurely deactivated catalyst is therefore a disruptive and expensive possibility.
A further problem experienced in refinery processes is fouling of items of process equipment by waxy or other solid residues that can build up in process equipment, such as pipework, vessels and columns. Such fouling reduces process efficiency by restricting flow rates and heat transfer.
An apparatus and method capable of predicting the effects of corrosion, fouling and catalyst deactivation of process equipment in the presence of different feedstocks would therefore be highly desirable.